Offshore Wind Power’s Eye-Popping Capacity Factors

Offshore wind power has hit a rough patch in Europe. There have been troubles with basking sharks and red-throated divers, but mostly there have been challenges in making the difficult technology economically viable. Nevertheless, a couple of items popped up in the last few days that provide a reminder as to what makes the offshore wind so exciting and potentially important.

First, there was the compilation of Danish offshore wind farm capacity factors published on the Energy Numbers website.

The Alpha Ventus wind farm, about 30 miles north of the German island of Borkum in the North Sea (image via Alpha Ventus)

The Alpha Ventus wind farm, about 30 miles north of the German island of Borkum in the North Sea (image via Alpha Ventus)

Capacity factor, as many EarthTechling readers know, is a measure of how much energy a generator produces over a period of time as a percentage of the maximum it could produce. So you take the total amount of energy produced in, say, a year, and divide by the amount of power the generator would produce had it run continuously at 100 percent.

Wind power capacity factors vary considerably by site, but generally people think around 30 to 35 percent when they talk about capacity factors for wind. But in Denmark in 2013, 13 offshore wind farms, totaling installed capacity of 1,271 megawatts, together had a capacity factor of 42.7 percent.

Yes, offshore wind power is costly now to build – too costly (Bloomberg New Energy Finance puts the megawatt-hour cost at $246). But with capacity factors of well over 40 percent, you can see the lure. You can see that with its ability to produce large amounts of power, offshore wind power deserves the effort and expense it will take to innovate and reduce costs.

The point was brought home, as well, last week with a press release from the Alpha Ventus offshore wind farm. Germany’s first wind farm – owned by EWE, E.On and Vattenfall – the 60-MW capacity Alpa Ventus began full operation in April 2010 and on Feb. 21 it announced it had reached 1 terawatt-hour of generation. And it’s doing better than expected:

The average yield of the offshore wind farm in 2011 through 2013 was 253.14 gigawatt-hours per annum, exceeding the forecast yield by approximately 10 per cent. The capacity factor of the wind farm of 48.1 per cent during this period is an outstanding result by international standards.

This is a pretty remarkable record of achievement – a beacon of hope, perhaps, amid the gloom that surrounds the sector.

Pete Danko is a writer and editor based in Portland, Oregon. His work has appeared in Breaking Energy, National Geographic's Energy Blog, The New York Times, San Francisco Chronicle and elsewhere.

  • Dave2020

    Guess what. . . . The only way to raise capacity factors even higher is to deploy new marine renewables (wind/wave) which incorporate integral energy storage. These designs float – cheaper to install and lower O&M costs.

    The thing is . . . Alpha Ventus may be as good as it will ever get, because an increasing penetration of wind (total installed capacity) will inevitably lead to more frequent curtailment, which means capacity factors will fall in future.

    If you store the surplus ‘harvest’, capacity factors can rise and you’ll need a far lower total installed capacity. That saves money on a whole-system basis.

    • Pete D

      Wind/wave is a discussion worth having, but really what this story was attempting to say was that capacity factors *don’t* need to increase. Capacity factors are great. It’s the cost of building and maintaining these things that’s the big issue. That’s what hasn’t evolved in the way people have expected.

      • Dave2020

        I’ve been addressing “the big issue” for years! (but people won’t listen)

        Capacity factors per se aren’t so critical, but my point is that as we get a greater total capacity of renewables deployed, widespread good wind will be going to waste, because of more frequent curtailment. Even at the current penetration in the US, Europe and China, GWhs of potential wind energy aren’t being harvested. There’s no profit in that!

        I don’t know what people expected, but in my view turbine design needed to ‘evolve’ radically and rapidly from the moment they first went offshore. The conventional stuff pictured above isn’t fit for purpose – period.

        Foundations and installation typically account for about 40% of the cost in shallow seas. The technical issues that made the Argyll and Atlantic Arrays uneconomic were the difficult sea bed and the frequency of wind and wave conditions that would have delayed installation! What do they expect? All pretty normal, I’d have thought! Water depths on some new sites are also twice that of the earlier UK wind farms – up from 25m to 50m.

        So, the answer is to mount a low c of g VAWT onto a four-float WEC, but the killer app is integral energy storage. These combined wind/wave designs don’t generate electricity on each vessel. They all pump water into storage and that in turn drives a handful of, say, 200MW generators in a centrally located service platform/power station. This electricity is dispatchable. It can rapidly respond to demand. You’d get the best price and you’d need less total installed capacity a for secure supply. Simple.

  • Kent Beuchert

    Wind is ALMOST as stupid as solar. And its non-dispatchability means monstrous side effect cots that wind enthusiasts generally lie about or totally ignore Reality
    will kill wind farms. You can’t fool everybody forever.

    • jeffhre

      “Reality will kill wind farms.” Yep, killing ’em! By negative 50 GW in the past four years! Dead as an exponentially growing door nail, and just as rational too!

    • Alec Sevins

      What exactly is stupid about solar? It’s the origin of almost every energy source on Earth when you trace it back. Wind turbines are a major eyesore but solar is a no-brainer considering all the existing man-made surfaces it could be installed on.

    • Aku Ankka

      Heh. You seem to be staying fool for life. Wind power is cheap, plentiful, and growing by leaps & bounds all over the globe. While fools like you are ranting and raving, hiding their head in sand, progress will happen. Wind and solar both make sense, especially compared to burning fossilized ferns and dinosaur remains.

  • Alec Sevins

    It’s also eye-popping to see vast swaths of nature desecrated and turned into industrial parks. But call it “green” and pseudo-environmentalists look the other way.

    • Aku Ankka

      Yes, but how does your comment relate to offshore (or onshore) wind power?
      Turbines look majestic and serene, producing clean energy and without harming nature much at all. especially relative to alternative modes of energy production (the only thing possibly having less effect being solar power).